At present many radio communication systems, such as portable telephone systems and radio MANs (Metropolitan Area Networks), are used. In addition, in order to further increase the speed and capacity of radio communication, lively discussions on next generation radio communication techniques are being conducted continuously.
For example, 3GPP (3rd Generation Partnership Project) which is a standardization organization proposed a communication standard which is referred to as LTE (Long Term Evolution) and by which communication can be performed by the use of a maximum of 20-megahertz frequency band. Furthermore, 3GPP proposed as a next generation communication standard for LTE a communication standard which is referred to as LTE-A (LTE-Advanced) and by which communication can be performed by the use of a maximum of 100-megahertz frequency band (see, for example, NPTL1).
In many radio communication systems a procedure under which one radio communication apparatus (mobile station, for example) transmits data to the other radio communication apparatus (base station, for example) from a state in which a radio resource used for data transmission is not assigned thereto is stipulated. Examples of such a procedure are (1) method by which random access is performed (see, for example, Paragraph 10.1.5 of NPTL2 or Paragraph 5.1 of NPTL3) and (2) method by which a scheduling request is transmitted (see, for example, Paragraph 5.2.3 of NPTL2 or Paragraph 5.4.4 of NPTL3).
When a mobile station performs random access to a base station, the mobile station transmits a signature which it selects at random from among a plurality of signatures to the base station as a random access preamble. The base station transmits a random access response as a response. After that, the mobile station transmits its identifier to the base station and the base station notifies the mobile station that it can recognize the mobile station. As a result, mobile stations go into a state in which they can be assigned radio resources individually by the base station for data transmission. With this method, however, random access contention may occur among a plurality of mobile stations. This leads to failure in a procedure.
With the method by which a mobile station transmits a scheduling request to a base station, the base station assigns in advance to the mobile station a control channel radio resource for transmitting the scheduling request. The mobile station uses the control channel radio resource for transmitting the scheduling request to the base station. The base station assigns radio resources for data transmission to mobile stations individually and notifies the mobile stations of the radio resource assigned thereto. As a result, each mobile station goes into a state in which it can perform data transmission.
With LTE-A, on the other hand, a reduction in delay time from a dormant state in which data transmission is not performed temporarily because of the intermittence of packet communication to the resumption of data transmission is under examination (see, for example, Paragraph 10.1 of NPTL4). (3) contention based uplink access is proposed as a method for realizing this (see, for example, NPTL5).
With the contention based uplink access from a mobile station to a base station, for example, the base station sets a radio resource (contention based radio resource) which a plurality of mobile stations can share for data transmission, that is to say, a radio resource which is not assigned individually to a plurality of mobile stations. When a mobile station detects the contention based radio resource, the mobile station uses the radio resource for data transmission without receiving particular permission from the base station. This reduces time which elapses before the beginning of data transmission by the mobile station. However, data transmission contention may occur among a plurality of mobile stations. This leads to failure in a procedure.
NPTL1: 3GPP (3rd Generation Partnership Project), “Requirements for Further Advancements for Evolved Universal Terrestrial Radio Access (E-UTRA) (LTE-Advanced)”, 3GPP TR 36.913, V8.0.1, 2009-03.
NPTL2: 3GPP (3rd Generation Partnership Project), “Evolved Universal Terrestrial Radio Access (E-UTRA) and Evolved Universal Terrestrial Radio Access Network (E-UTRAN); Overall description”, 3GPP TS 36.300, V9.0.0, 2009-06.
NPTL3: 3GPP (3rd Generation Partnership Project), “Evolved Universal Terrestrial Radio Access (E-UTRA) Medium Access Control (MAC) protocol specification”, 3GPP TS 36.321, V9.1.0, 2009-12.
NPTL4: 3GPP (3rd Generation Partnership Project), “Feasibility study for Further Advancements for E-UTRA (LTE-Advanced)”, 3GPP TR 36.912, V9.0.0, 2009-09.
NPTL5: 3GPP (3rd Generation Partnership Project), “Contention based uplink transmissions”, 3GPP TSG-RAN WG2 #66bis R2-093812, 2009-06.
As stated above, there are a plurality of methods for beginning data transmission from a state in which a radio resource used for data transmission is not assigned individually. However, how to use these access methods is problematic. In particular, if a contention based radio resource is set as proposed in the above NPTL5, the relationship between the method using the contention based radio resource and the other access methods is problematic.